A strainer used in a submergible pump of prior art has usually been made in a cylindrical tube form having a plurality of longitudinal slits or a plurality of perforations on the cylindrical surface through which the liquid is sucked into the pump. Such strainer has been generally made by a casting process or of a sheet metal and directly attached to a pump body at its suction opening.
The slits or perforations are choked with foreign materials during use and, when soft items such as fibrous foreign materials are caught in the slits or perforations, the ends of such foreign fibrous materials may become entangled with each other thereby making it difficult and troublesome to remove them from the strainer. Also, such strainer is likely to be choked with other foreign materials and, therefore, the length of slits or number of perforations is generally increased to provide some surplus operating time whereby the axial length of the strainer is lengthened which causes a condition wherein the water cannot be satisfactorily pumped out close to the water bottom because the position of the suction opening is made higher due to the increased axial length of the strainer.
Also, when the operation of the submergible pump is stopped, the delivery water containing foreign materials may flow backward to cause clogging of the strainer so that further actuation of the pump becomes impossible.
Such clogging of the strainer due to backward flow of the delivery water is difficult to clear if the foreign materials trapped these contain fibrous items because pulling the trapped fibrous materials from the outside of the strainer will cause them to be tightly pushed into the slits or perforations together with other foreign materials. Therefore, it is necessary to dismantle the strainer for the purpose of cleaning the trapped materials therefrom.